The blast happened in the central part of the southern Helmand province during an escort operation, the ministry said in a statement.
It takes the number of British soldiers killed in Afghanistan to 148 since the U.S.-led invasion in 2001.
The soldiers from the 1st Battalion The Rifles were pronounced dead by a doctor in an emergency response helicopter. No more details of the incident or those killed were released. The victims' families have been informed.
Commander Paula Rowe, spokeswoman for the Helmand force, said in a statement: "Today has been incredibly sad for the whole of Task Force Helmand, and particularly for The Rifles. We will all feel the loss of these brave soldiers."
Britain has about 8,000 soldiers in Afghanistan fighting an increasingly bold Taliban insurgency
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